1. Field of the Invention
The present invention relates to a driver IC for driving an electro-optical element such as liquid crystal or the like, an electro-optical device and electronic equipment, and particularly to an improvement of temperature compensation necessary to drive an electro-optical element.
2. Description of Related Art
For example, taking liquid crystal as an example of the electro-optical element, the liquid crystal has temperature-dependence, and the optical transmissivity of the liquid crystal is varied even under application of the same voltage if the environmental temperature is varied. Therefore, various temperature compensation countermeasures have been hitherto taken. One of these countermeasures is to linearly interpolate the voltage to be applied to the liquid crystal, thereby performing the temperature compensation. As a method of implementing this countermeasure, the linear interpolation is executed by selecting any one of two or more temperature gradients or combining these temperature gradients.
In this linear interpolating method, since the temperature gradient is constant over the overall region from a low temperature area to a high temperature area, it is not necessarily coincident with the temperature dependence of the actual liquid crystal, and it is impossible to perform the temperature compensation with high precision.
Although the temperature dependence of the liquid crystal has an influence on not only the applied voltage-transmissivity characteristic but also on other parameters, no temperature compensation is carried out on these other parameters.
Furthermore, a temperature sensor for detecting the environmental temperature is indispensable to perform this kind of temperature compensation. Since the temperature sensor aims to detect the temperature for the temperature compensation of liquid crystal, it should be originally used to detect the temperature of the liquid crystal itself, however, it is actually impossible to detect the temperature of the liquid crystal.
Therefore, the temperature sensor must be provided outside a display panel, and a physical distance occurs between the liquid crystal and the temperature sensor. The physical distance is increased as the size of the liquid crystal panel is increased, and thus the temperature sensor detects the temperature at some place which is different in temperature from the temperature of the liquid crystal.
An objective of the present invention is to provide a driver IC, an electro-optical device and electronic equipment which can perform more accurate temperature compensation in conformity with the temperature dependence of an electro-optical element.
Another objective of the present invention is to provide an electro-optical device and electronic equipment in which a temperature sensor is installed in a driver IC to perform temperature detection having a less difference from the temperature of liquid crystal, thereby performing more accurate temperature compensation.
According to a first aspect of the present invention, there is provided a driver IC for driving an electro-optical element comprising: a power circuit for outputting a voltage in accordance with the temperature-voltage characteristics; an electrical volume for varying an output voltage from the power circuit; a temperature detector for detecting an environmental temperature; and a correction table for storing an electrical volume control value corresponding to a temperature detected by the temperature detector. The power circuit comprises: a first power circuit having a first temperature-voltage characteristic; a second power circuit having a second temperature-voltage characteristic; and a temperature gradient selection circuit for outputting a voltage conforming with a desired temperature gradient characteristic based on output voltages from the first and second power circuits. The temperature detector detects an actual temperature based on the first and second temperature-voltage characteristics, and adjusts the output voltages from the first and second power circuits at the electrical volume according to the electrical volume control value in the correction table and outputs the adjusted voltages, the electrical volume control value corresponding to an actual temperature detected by the temperature detector. This aspect of the invention makes it possible to provide a low temperature area, a room-temperature area, and a high temperature area with different temperature gradients, to implement applied voltage compensation conforming with the temperature dependence of an electro-optical element, such as curved line interpolation other than the linear interpolation, for example.
According to a second aspect of the present invention, there is provided a driver IC for driving an electro-optical element comprising: an oscillator for outputting an oscillation frequency which is variable by an electrical volume; a temperature detector for detecting an environmental temperature; and a correction table for storing an electric volume control value corresponding to a temperature detected by the temperature detector. The oscillation frequency of the oscillator is variable by adjusting the electrical volume based on the electrical volume control value in the correction table which corresponds to an actual temperature detected by the temperature detector. This makes it possible to change a frame frequency according to temperature, so that a frame frequency following the characteristic of an electro-optical element wherein the reaction speed depends on temperature can be set.
According to third aspect of the present invention, there is provided a driver IC for driving an electro-optical element comprising: an oscillator; a gray scale clock generator for generating a gray scale clock based on an oscillation frequency of the oscillator; a gray scale pulse generator for generating a plurality of gray scale pulses each having a pulse width which depends on a gray level value, based on the gray scale clock from the gray scale clock generator; a temperature detector for detecting an environmental temperature; and a correction table for storing a correction value for a gray scale pulse width which corresponds to a temperature detected by the temperature detector. The gray scale pulse generator is capable of varying pulse widths of a plurality of gray scale pulses based on a correction value for a gray scale pulse width in the correction table which corresponds to an actual temperature detected by the temperature detector. This makes it possible to prevent the deterioration of gray levels due to temperature by changing the pulse width of gray scale pulses depending on temperature, even when there is a temperature dependence characteristic wherein gray level values are different from each other when the same voltage is applied to the electro-optical element at a room temperature and a lower temperature.
According to a fourth aspect of the present invention, there is provided an electro-optical device comprising: a panel having an electro-optical element between a first substrate and a second substrate; and a driver IC which is mounted on the first substrate and drives the electro-optical element. The driver IC comprises: a temperature detector for detecting an environmental temperature; and a temperature compensation circuit for performing temperature compensation necessary for driving the electro-optical element, based on an actual temperature detected by the temperature detector. First and second electrodes are respectively formed on the first and second substrates to face the electro-optical element. At least one of the first and second electrodes is connected to a terminal of the driver IC mounted on the first substrate and has a redundant portion which extends from a position of the terminal to a back surface of the driver IC. This aspect of the invention makes it possible to detect a temperature having only a slight difference from the temperature of liquid crystal by the temperature detector in the driver IC, since the temperature of the electro-optical is transmitted through the electrode and the redundant portion thereof to the back surface of the driver IC. Therefore, the precision of the temperature compensation can be enhanced.